Diamond-Blackfan anemia (DBA) is a rare pure red-cell aplasia that presents early in infancy. Virtually every aspect of DBA is heterogeneous, posing considerable challenges to efforts to understand and treat this disease. Approximately 25% of DBA cases are linked to mutations in the ribosomal protein $19 gene, whereas the remaining cases are of unknown etiology. A goal of this application is to address the molecular basis of DBA, focusing on the role of Rps19 in ribosome synthesis. Our studies in yeast have shown that Rps19 is required for the maturation of 40S ribosomal subunits. We plan to extend these studies and examine ribosome synthesis in cell lines from DBA patients. We have also identified several other yeast ribosomal proteins that appear to cooperate with Rps19 in the maturation of 40S subunits. If patients with normal Rps19 were defective in ribosome synthesis, genes encoding proteins that cooperate with Rps19 would become candidate genes for disease-causing mutations. Our studies in yeast have also pointed to a need for functional testing of putative disease-causing mutations identified in Rps19 genes from DBA patients. Finally, we will study the relationship between ribosome synthesis and bone marrow failure in a transgenic mouse model. The specific aims of this application are to: 1. continue studies characterizing the effect of DBA missense mutations on the function of the Rps19 protein in yeast. 2. determine if there are defects in the protein synthetic machinery in cell lines from DBA patients. 3. determine which ribosomal proteins depend on Rps19 for their assembly into 40S ribosomal subunits. 4. characterize the phenotype of mice hemizygous for LAMR1 including hematological analysis, cancer incidence, and the presence of other congenital abnormalities.